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JOYSTICK
Posted Date: 22 Feb 2008 Resource Type: Articles/Knowledge Sharing Category: How things work
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Posted By: syam s kurup Member Level: Silver
Rating:  Points: 5
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JOYSTICK
A joystick is used mainly to control on-screen movement in computer games. It feeds three kinds of information to the computer–horizontal movement, vertical movement, and on-off signals when the action buttons are pressed. Joysticks designed for flight-simulator players have an extra control called a top hat on the top of the stick, providing an additional set of thumb-operated horizontal and vertical movement controls. Joysticks were once the ultimate in controllers for electronic gamers, but other types of controllers are increasingly becoming popular. For driving games there are realistic steering wheels which often come with a separate foot pedal unit for accelerating and braking. One recent development is force feedback technology, found in some high-end joysticks and steering wheels. Instead of just passively being pushed around, a force feedback controller has motors that make the controller actually move in your hand, reflecting the on-screen action.
WORKING
Joysticks take something entirely physical–the movement of your hand-and translate it into something entirely mathematical–a string of ones and zeros (the language of computers). With a good joystick, the translation is so flawless that one completely forgets about it. When one is really engaged in a game, one feels that there is direct interaction with the virtual world.
The technology has evolved a great deal from the first game console designs to the sophisticated force feedback models available today.
The basic idea of a joystick is to translate the movement of a plastic stick into electronic information a console can process. Joysticks are used in all kinds of machines, including F-15 fighter jets, heavy earth moving equipment, cranes, bulldozers, wheelchairs and industrial automation. The same principles applicable for game console joysticks also apply to other sorts of joysticks.
The various joystick technologies differ mainly in how much information they pass on. The simplest joystick design, used in many early game consoles, is just a specialised electrical switch.
This basic design consists of a stick that is attached to a plastic base with a flexible rubber sheath. The base houses a circuit board that sits directly underneath the stick. The circuit board is made up of several ‘printed wires’, which connect to several contact terminals. Ordinary wires extend from these contact points to the computer.
The printed wires form a simple electrical circuit made up of several smaller circuits. The circuits just carry electricity from one contact point to another. When the joystick is in the neutral position–when one is not pushing one way or another–all but one of the individual circuits are broken. The conductive material in each wire doesn't quite connect, so the circuit can't conduct electricity.
Each broken section is covered with a simple plastic button containing a tiny metal disc. When one moves the stick in any direction, it pushes down on one of these buttons, pressing the conductive metal disc against the circuit board. This closes the circuit–it completes the connection between the two wire sections. When the circuit is closed, electricity can flow down a wire from the game console, through the printed wire, and to another wire leading back to the console.
When the game console picks up a charge on a particular wire, it knows that the joystick is in the right position to complete that particular circuit. Pushing the stick forward closes the forward switch, pushing it left closes the left switch, and so on. In some designs, the computer recognizes a diagonal position when the stick closes two switches (for example, closing the forward switch and the left switch simultaneously would mean a forward/leftward diagonal position). The firing buttons work exactly the same way–when you press down, it completes a circuit and the console recognizes a fire command. This design communicates joystick motion in a sort of shorthand–it processes movement as absolute values instead of subtle gradations. In other words, it can't distinguish between pressing forward on the stick a little bit and pushing it as far as it will go–there is only one value for forward.
This is fine–even ideal–for some games. It is the perfect design form something like Pac Man or Tetris, for example. But it can be fairly limiting for other games, such as flight simulators.
In order to communicate a full range of motion to the computer, a joystick needs to measure the stick's position on two axes–the X-axis (left to right) and the Y-axis (up and down). Just as in basic geometry, the X-Y coordinates pinpoint the stick's position exactly.
In the standard joystick design, the handle moves a narrow rod that sits in two rotatable, slotted shafts. Tilting the stick forward and backward pivots the Y-axis shaft from side to side. Tilting it left to right pivots the X-axis shaft. When you move the stick diagonally, it pivots both shafts. Several springs center the stick when you let go of it.
To determine the location of the stick, the joystick control system simply monitors the position of each shaft. The conventional analog joystick design does this with two potentiometers, or variable resistors. The diagram below shows a typical arrangement.
Each potentiometer consists of a resistor, in the form of a curved track, and a movable contact arm. The computer power supply conducts electricity to the input terminal, through the curved resistor, through the contact arm and back to the joystick port on the console.
By moving the contact arm along the track, you can increase or decrease the resistance acting on the current flowing through this circuit. If the contact arm is on the opposite end of the path from the input connection terminal, electricity will have to flow through a long length of resistor, so it will face maximum resistance. If the contact arm is near the input terminal, the potentiometer will have minimal resistance.
Each potentiometer is connected to one of the joystick shafts so that pivoting the shaft rotates the contact arm. In other words, if you push the stick all the way forward, it will turn the potentiometer contact arm to one end of the track, and if you pull it back toward you, it will turn the contact arm the other way.
Varying the resistance of the potentiometer alters the electrical current in the connected circuit. In this way, the potentiometer translates the stick's physical position into an electrical signal, which it passes on to the joystick port on the computer.
This electrical signal is totally analog–it is a varying wave of information, like a radio signal. In order to make the information usable, the computer needs to translate it into a digital signal–a strict numerical value.
In the conventional system, a card (a printed circuit board) inside the game console handles this with a very crude analog-to-digital converter. The basic idea is to use the varying voltage from each potentiometer to charge a capacitor, a simple electrical device that stores electricity. If the potentiometer is adjusted to offer more resistance, it will take the capacitor longer to charge; if it offers less resistance, the capacitor will charge more quickly.
By discharging the capacitor and then timing how long it takes it to recharge, the converter can determine the position of the potentiometer, and therefore the joystick. The measured recharge rate is a numerical value the computer can recognize. The console performs this operation whenever it needs to get a read on the joystick.
You can potentially apply this system to an infinite variety of controls by connecting a potentiometer to different rotating components. For example, conventional steering wheel controllers work exactly the same way, with the wheel rotating the potentiometer contact arm directly. Some joysticks use an additional potentiometer for a Z-axis, activated by rotating the stick itself.
There are a couple of big problems with the conventional analog joystick system. First of all, the crude analog-to-digital conversion process isn't very accurate, since the system doesn't have a true analog-to-digital converter. This compromises the joystick's sensitivity somewhat. Secondly, the host console has to dedicate a lot of processing power to regularly poll the joystick system to determine the position of the stick. This takes a lot of power away from other operations.
Joystick manufacturers have addressed these problems in a couple of different ways. One solution is to add a sensitive analog-to-digital converter chip in a specialised game adapter card or in the joystick itself. In this system, the converter spits out digital information directly to the computer, which improves the accuracy of the stick and reduces the work load on the host processor. These new joystick models can usually connect to USB ports, which also improves speed and reliability.
Another solution is to skip the analog potentiometer technology all together. Many newer controllers use optical sensors to read stick movement digitally. In this system, the two shafts are connected to two slotted wheels. Each wheel is positioned between two light-emitting diodes (LEDs) and two photocells (the graphic only shows one photocell, LED pair for the sake of simplicity). When light from each LED shines through one of the slots, it causes the photocell on the other side of the wheel to generate a small amount of current. When the wheel rotates slightly, it blocks the light and the photocell doesn't generate current (or it generates less current).
When the shaft pivots, it spins the wheel, and the moving slots repeatedly break the light beam shining on the photocell. This causes the photocell to generate rapid pulses of current. Based on the number of pulses that the photocells have generated, the processor knows how far the stick has moved. By comparing the patterns coming from both photocells monitoring one wheel, the processor can figure out which way the stick is moving. This is the same basic system used in many computer mice.
The basic idea of a force feedback joystick (also called a haptic feedback joystick) is to move the stick in conjunction with onscreen action. For example, if you are shooting a machine gun in an action game, the stick would vibrate in your hands. Or if you crashed your plane in a flight simulator, the stick would push back suddenly.
Force feedback joysticks have most of the same components as ordinary joysticks, with a few important additions–an onboard microprocessor, a couple of electrical motors and either a gear train or belt and pulley system.
The joystick has a built-in ROM chip that stores various sequences of motor movement. For example, it might have a machine gun sequence that instructs the motors to rapidly change direction, or a rocket launcher sequence that instructs the motor to shift the joystick backward suddenly and then forward again. The game software requests a particular sequence, and the computer transmits the request to the joystick's onboard processor, which brings up the appropriate data from its own memory. This reduces the work load on the console and makes for faster reaction times.
As joysticks continue to evolve, manufacturers will take force feedback technology to whole new levels. This is great for avid gamers, of course, but it could also have a big effect on the rest of the population. Force feedback controller technology could lead to significant changes in industrial machinery, wheelchairs and other equipment for handicapped people, and even medical care. Researchers are also developing force feedback controllers to let people ‘feel’ the Internet as they surf.
The possible applications are endless. In the future, joysticks could be as ubiquitous as computer keyboards are today.
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Responses
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| Author: Moncy 24 Feb 2008 | Member Level: Silver Points : 2 | Yea, it's good to use a joy stick but not economical. Its because it dosen's last long..Same is the case with mobile phone's joystick also.
| | Author: Moncy 24 Feb 2008 | Member Level: Silver Points : 2 | Yea, it's good to use a joy stick but not economical. Its because it dosen's last long..Same is the case with mobile phone's joystick also.
| | Author: Avdhut Sonpethkar 25 Feb 2008 | Member Level: Gold Points : 3 | this is a very good information you have given here syam. I knew that the joystick can only be used for playing nothin other than that, now i know its wide range of application too. I used joystick only to play video games in playstation or PC.
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